This invention relates generally to methods for removing adherent materials, for example, undesirable residues, precipitates, scale and other materials from internal surfaces such as pipes and tanks, especially internal surfaces used to transport or deliver liquids in closed systems. In particular, the method employs an improved cleaning media comprising core/shell particles.
For various types of structures, it is often desirable to remove a coating that has been formed on an interior surface area. Numerous techniques exist for removing paint, rust, scale, biogrowth and other adherent materials from virtually any type of surface. Surface cleaning or stripping methods range from mechanical abrasion to the use of strong chemicals and involve varying degrees of time, effort and expense. This invention relates to compositions and methods for removing unwanted deposits or build-up on surfaces of internal surfaces in fluid delivery/transport systems (referred to herein as xe2x80x9cfluid transport systemsxe2x80x9d) or parts thereof, including conduits, tanks, and related equipment, for example, the throughput parts of pumps. The invention is particularly useful for cleaning substantially closed systems. Large quantities of fluids with suspended, dispersed or dissolved materials (hereinafter referred to as xe2x80x9ccarried materialsxe2x80x9d) are often circulated through fluid transport systems and over time the material may deposit or settle on various interior surfaces of the fluid transport system. For example, paints, inks, or components thereof are circulated or re-circulated in piping of delivery systems in industrial manufacturing plants. During the course of normal operation, the carried materials in a fluid may build up or deposit on the inside of fluid delivery systems, especially in areas of reduced flow such as in filters, tees, elbows and valves. As a consequence fluid delivery systems are cleaned on a periodic basis to remove the unwanted carried materials adhering to the insides of pipes, tubing, filters and/or valves. Since these systems are enclosed, at least to a substantial extent, removal of unwanted material adhering to the insides of tubes, pipes and other conduits is difficult to achieve because access is difficult, and, in fact, frequently it is difficult even to determine the extent of cleaning.
Industrial applications where internal surfaces need to be cleaned include, for example, food (e.g. dairy and beverages), pharmaceuticals, inks and pigments, paints, oil pipelines, oil refinery lines, power plants, marine lines in ships, and polymer and chemical manufacturing pipelines in general.
For example, coating or paint delivery systems are utilized for the finishing of a wide variety of manufactured items such as motor vehicles, household appliances and the like. A typical industrial paint delivery system may comprise a central paint supply having a number of painting stations communicating therewith. Such paint delivery systems can selectably deliver a variety of different paints to a given painting station and include complex fluid pathways involving various tanks, pumps and conduits. These paint delivery systems tend to become clogged with encrustations in the course of their use and such deposits can decrease and even block the flow of paint there through. Such clogging is occasioned by deposits of pigment, resins or other components of the paint within the tanks and lines of the system. In addition to causing clogging, such deposits can also contaminate the paint color, and can cause surface defects in the finished, painted product. Cleaning the paint delivery system reduces the amount of surface repairs to paint finishes. The build-up of residues necessitates periodic cleaning of paint delivery systems and because of the complexity of the systems and the necessity of avoiding expensive downtime, it is generally preferable that such systems be cleaned without or with minimum disassembly. The prior art approach to cleaning involves passing a variety of solvents, detergents or other cleaners through the system, and tends to involve numerous steps and multiple compositions. It should be noted that these processes often do not provide full removal of deposits, particularly pigment residues.
A typical prior art process can involve flushing five or more different cleaning compounds of varying polarity through the paint system and can include 30 separate operational steps. The numerous cleaning compounds are needed in order to fully remove the residues in the system and to ensure compatibility of any cleaner residue remaining in the system with subsequently introduced paint. As a result, the system must be sequentially rinsed with various materials in a predetermined order such that the final rinse is with a paint-compatible thinner. Clearly, it would be most advantageous to reduce the number of steps by utilizing a cleaning composition which is fully paint-compatible, and to improve the efficiency of the process by utilizing a composition capable of removing all residues. In addition to toxicity and waste disposal problems, another of the shortcomings of prior-art paint system cleaning, especially ones requiring organic solvents, is that they do not provide sufficient cleaning action, particularly with regard to encrusted pigment deposits and, as a consequence, long flush times and/or repeated cleaning cycles have been generally required.
It has been known to utilize abrasive materials to clean closed lines and one such process is disclosed in U.S. Pat. No. 4,572,744 which describes the use of sand or similar material entrained in a flow of air to clean the interior of boiler tubes. Also mentioned in the ""744 patent is the similar use of liquid based abrasive slurries to clean pipes. Various attempts have been made to utilize abrasive based materials for cleaning paint lines and it is known to employ mica, or sand particles in conjunction with a flush liquid to scour the interior of paint lines. Problems have arisen with the use of such inorganic abrasives insofar as they can be relatively hard and tend to damage or clog pumps and passageways through which they flow. Additionally, such inorganic abrasive materials are also relatively dense and tend to settle out of a cleaning fluid unless vigorous agitation is maintained or thickeners are added to increase the solution viscosity.
For example, it is known to utilize a specific paint system cleaning composition comprised of sand or mica suspended in a solution of xylene and methyl isobutyl ketone thickened with a resinous material. Compositions of this type present problems insofar as the resin and abrasive are difficult to rinse from the system thereby presenting problems of contamination, particularly when the resin is not compatible with subsequently employed paint compositions. Additionally, the viscous composition presents problems of waste disposal insofar as the resin is difficult to incinerate and inhibits the ready evaporation and recovery of the xylene and ketone. Obviously, the inorganic abrasive residue presents significant waste disposal problems insofar as it cannot be readily incinerated.
U.S. Pat. No. 4,968,447, to Dixon and Maxwell, proposes the use of polymeric particulates made of polypropylene, polyethylene, polyvinylchloride, polytetrafluoroethylene, and various other hydrophobic organic polymers and copolymers.
Organic, polymeric materials are not generally thought of as being abrasive; however the present invention relies in part upon the counter intuitive finding that organic materials can function very well to facilitate the cleaning of encrustations from paint delivery systems. Dixon et al. utilize polymeric particles of relatively low density that can be maintained in suspension without resort to thickeners or vigorous agitation. Dixon et al. state that, although these organic materials perform an excellent job of cleaning residues from paint lines, they are not sufficiently abrasive to damage pumps, valves and the like.
The rheological additive xe2x80x9cViscotrolxe2x80x9d, available from Mooney Chemicals, Inc. of Cleveland, Ohio, has been described as a particulate derivative of castor oil, apparently lightly crosslinked, which may be added to a re-circulating paint cleaning system to act as a mild abrasive. After use, their removal from the system is assured by introducing an alcohol or other solvent which is absorbed by the particles, causing them to swell so they may be readily separated by filtering. xe2x80x9cViscotrolxe2x80x9d is referred to as a xe2x80x9crheological materialxe2x80x9d by Bergishagen et al. in U.S. Pat. No. 5,443,748, which employs it in several examples for cleaning paint delivery systems.
U.S. Pat. No. 4,572,744 discloses that the Sandjet(copyright) process is a well known and successful process for the in-situ cleaning of the interior surfaces of conduits used for the transport and/or processing of fluids, solids or a mixture thereof. The conduits thus cleaned include fired heater tubes used in hydrocarbon or chemical processing, pipelines, heat exchange tubes and the like. In the practice of the Sandjet(copyright) process for such in-situ cleaning operations, cleaning particles are entrained in a propelling fluid stream and are introduced into the conduit to be cleaned at a velocity sufficient to effect the desired cleaning action. In furnace tube applications, the Sandjet(copyright) process is used to decoke and clean furnace tubes. By the use of steel shot or other suitable cleaning materials, the Sandjet(copyright) process can achieve a desirable decoking action without undue abrasion of the straight sections or of the return bends of such furnace tubes. Dominick in U.S. Pat. No. 4,572,744 discloses that improvements are needed in the art to enable the Sandjet(copyright) process to be employed with enhanced reliability in the decoking of difficult-to-remove deposits, without resulting in an unacceptable level of abrasion of the tubes, particularly the bends of said tubes. One approach to the development of improvements enhancing the Sandjet(copyright) process resides in the use of new cleaning agents to achieve an advantageous balance of desired cleaning action and undesired abrasive action. Some such agents would have an improved cleaning action over that achieved by steel shot, while avoiding the abrasive action of materials such as flint.
U.S. Pat. Nos. 5,505,749 and 5,509,971 to Kirshner et al. disclose the use of a major amount of a granular relatively soft abrasive having a Mohs hardness of less than 4 and a minor portion of a granular hard abrasive having a Mohs hardness of greater than 5. U.S. Pat. No. 5,234,470 to Lynn et al. discloses a granulated composite, in particular, a flexible open cell water-foamable material and an abrasive mineral such as garnet.
In spite of the above known compositions and techniques, the cleaning art for fluid transport systems is in need of a better way to remove as completely as possible the deposits and build-up from the tubes, piping, pumps and filters of the fluid transport systems. It would be desirable to provide cleaning methods and compositions that would completely clean the old deposits and buildup from the inside of such fluid transport systems, without damaging any permanent surfaces.
It would be desirable to be able to clean an internal surface of fluid delivery or transport systems, and parts thereof, more rapidly and effectively without damaging the underlying surface. It would also be desirable to be able to more finely control or tailor the abrasive properties of the media to balance its ability to remove a particular coating without attacking a particular surface material.
It would be desirable to accomplish this without using chemicals that present environment or health problems. It would be desirable to be able to economically manufacture and customize such cleaning particles for a particular application.
The above objects are achieved by providing an abrasive media that comprises a polymeric core surrounded by a layer or shell of hard inorganic particles. The media can be propelled against or along the internal surface by a fluid carrier medium, including liquids, gases, or mixtures of gases and liquids, to remove the unwanted surface material.
This invention can be used for removing adherent materials, for example, residues, deposits, scale, soot, fouling, contaminants, biogrowth, and other unwanted materials from various internal surfaces. Contaminants to be removed from a surface may include any objectionable substance attached to the surface.
In accordance with the present invention, there is provided a method of cleaning interior surfaces of fluid delivery or transport systems and lines and parts thereof The method comprises passing through the system an abrasive cleaner composition comprising at least one fluid carrier containing abrasive particles as described herein to abrade the deposited material to be removed from the interior surfaces of the system.
In one embodiment, the abrasive media may be propelled by a liquid along a surface such as the interior walls of a pipe, to remove adherent materials.
The compositions of the present invention may be advantageously utilized in cleaning the lines and tanks of manufacturing plants as well as for other cleaning purposes where some degree of abrasive action is required. The relatively low viscosity of the cleaning compositions of the present invention simplifies their disposal or recycling. The use of the abrasive particles in an aqueous vehicle avoids the use of toxic solvents. The abrasive particles of this invention are particularly effective in removing adherent material while not damaging the surfaces being cleaned. These and other advantages of the present invention will be readily apparent from the detailed description which follow.